This application claims priority to an application entitled xe2x80x9cDEVICE FOR SETTING REFERENCE WAVELENGTH IN OPTICAL CHANNEL MONITORING MODULExe2x80x9d, filed with the Korean Industrial Property Office on Feb. 2, 2000 and there duly assigned Serial No. 5120-2000.
1. Field of the Invention
The present invention relates generally to an optical communication system, and more particularly to an optical channel-monitoring module in a WDM (Wavelength Division Multiplex) optical communication system.
2. Description of the Related Art
As the demand for optical communication systems has increased, there has arisen a need for the development of wavelength monitoring techniques. An optical channel-monitoring module is typically used to monitor the transmission of an optical signal in a WDM optical network. The function of a monitoring module is to provide information that is used to repair and maintain the optical communication system, including the intensities of the optical signals in the channels, the multiplexed optical signal, the optical signals prior to demultiplexing, and the demultiplexed optical signal.
There are various methods that implement the optical signal monitoring function in accordance with the prior art. Among them, a monitoring module using the wavelength variable filter is widely used. In this method, a preset reference wavelength is introduced to compensate for the instability of a transmission wavelength so that an accurate wavelength can be derived from the reference wavelength. Here, the use of a light source to generate a stable wavelength is a very important aspect in the optical channel monitoring function. The output of an active device, i.e., a laser diode, is typically used as a reference wavelength. However, the implementation of this method requires additional devices, i.e., a stabilizing circuit for stabilizing the output wavelength of the laser diode, thus imposing economic constraints.
Another conventional method uses the position of an ASE (Amplified Spontaneous Emission) light filtered by the fiber gratings in an optical fiber amplifier as a reference wavelength to control the wavelength characteristics. Yet, this method is ineffective in detecting the reference wavelength in a photodiode when the intensity of the input ASE light is low in the absence of an optical fiber amplifier. Thus, an additional device, i.e., optical amplifier, is required.
As is apparent from the above, there is a need for an improved optical wavelength reference and control techniques that avoid additional component requirements and other problems associated with the prior art devices.
It is, therefore, an object of the present invention to provide a reference wavelength setting device that is inexpensive and that provides a stable reference wavelength needed for a channel monitoring function.
It is another object of the present invention to provide a reference wavelength setting device for providing a stable reference wavelength without using the ASE light of an optical fiber amplifier.
To achieve the above objects, there is provided a reference wavelength setting device in an optical channel-monitoring module with a variable filter, comprising: a light-emitting device for outputting wide-band light upon receipt of a driving voltage; a light-emitting device driver for switching the driving voltage to the light-emitting device upon receipt of an emission-on signal; a fiber grating for reflecting only the light at a particular reference wavelength range from the wide-band light received from the light emitting device; and, an optical distributor for feeding the wide-band light received from the light-emitting device to the fiber grating and outputting the light at the reference wavelengths reflected by the fiber grating.
Another object of the invention is to provide an optical coupler for outputting the light at the reference wavelengths received from a reference wavelength provider to the variable filter.
Further object of the invention is to provide a controller for selectively outputting the emission-on signal to the light emitting device driver in order to monitor the input optical signal.